1. Field of the Invention
The present invention is directed to a common bus multinode sensor system that allows multiple remote units to simultaneously transmit over the common bus using frequency division multiplexing and, more particularly, to a system that provides power to the remote units via the bus and allows low speed digital, low frequency analog signals and high frequency analog signals to be transmitted over the bus to receivers which demodulate the analog signals and decode the digital signals.
2. Description of the Related Art
Closed loop communication systems for facilities such factories and nuclear power plants require the capability of transmitting digital, low frequency analog and high frequency analog signals from a plurality of spaced apart points to a central location through an environment full of electromagnetic noise. Such systems typically require that the communication medium such as a twisted wire pair, coaxial cable or optical light guide be spread out through a very large complex requiring a media up to two kilometers in length. Prior art methods of providing such closed loop networks typically provide synchronous data transmission over a transmit channel and a receive channel. These systems poll each remote unit separately and, as a result, operate using a time division multiplexing scheme. The use of time division multiplexing does not allow plural sensors to be sampled simultaneously. The prior art systems also require power supplies at each remote unit producing ground loop problems as well as requiring that extra power wires be provided to the remote units.